Sinclair ZX80 / ZX81 / Z88 Forums

Just a final update. New ULA 81 fitted in a socket from Charles at vRetro who I have to thank for getting the chip from New Zealand to the UK in under a week from ordering!! I still have a few bits to do, check mic and ear sockets for correct operation, replace regulator with something more modern, ...

Oh ye of little faith. I knew i should have put a pic up of the other side of the board to

Couldn't agree more about lighting and magnification, my eyes are all about extra photons these days.

Mike

Just an update. Had some time today to have a go at removing the ULA. Managed to get it out without resorting to chopping legs with solder sucker and some braid. It took me about 40 minutes working slowly and carefully, would have been faster and easier with more suitable tools and the fresh eyeball...

I don't think I've removed a 40 pin ic since the late 80's (my main era of component level repair) and all the desoldering capabilities I have access to these days are 'simple' hot air aimed at surface mount these and so I quite understand trying to be as 100% as possible before opting on the 'nucle...

Thanks for the reply. I've just checked, less than 0.4 Ω so looking like the ULA (don't get a lot less than that shorting the leads on the Fluke). I know genuine one's are in short supply. Is one of the modern ones that 'copy' the 2C210E ula with a few bells and whistles a good choice for replacemen...

OK, just got chance to run this. My results:

All ran as normal and I saw it gradually counting down the page, albeit with the corrupted characters.

Thanks for the suggestion, I did consider that while testing yesterday but none of the little loops came to mind (it's been 40 years lol) and I was a little time limited. I'll try this on Monday when back at work and post results.

Thanks for taking a look. I take it I'm probably looking at eprom or ula?

Hopefully this is clear enough

Hi Xavier, thanks for even more helpful information. I typed 'R' and got the image as shown below, followed by V then Newline and got what is shown in the second image. I checked the resistors from 18 to 26, they all read similar values around 1K. I also checked the diodes from the keyboard, again a...